Effortful control (EC), which reflects the self-regulatory aspect of early childhood temperament, develops considerably in the first five years of life. Optimal EC by preschool age is desirable because it affects children's socioemotional adjustment at school entry, which in turn predicts behavioral and academic growth throughout middle childhood and adolescence. Previous research has identified selected characteristics of children, their families, and their neighborhoods that influence early EC. However, only one such study has examined all three ecological contexts at once, and it was not designed for multilevel data analysis. Following Bronfenbrenner's bioecological model of development, we make use of a multilevel data set that was designed to study child development in context. Hierarchical linear modeling is used to analyze children sampled from diverse neighborhoods throughout Chicago. We select a cohort of children that was followed from birth/infancy to 6 years of age, and test the explanatory power of characteristics from three environmental contexts: the mother-child relationship, the family, and the neighborhood. Mother-child relationship characteristics include corporal punishment, maternal hostility, maternal warmth, and maternal depressive symptoms. Family characteristics include family instability, family conflict, inter-parental violence, and household chaos. Neighborhood characteristics include collective efficacy, disorder, and access to safe play spaces. In testing whether these environmental characteristics influence children's developing EC (adjusting for child, family, and neighborhood demographic characteristics), special attention will be paid to the possibility that they are differentially associated with two facets of EC - delay and motor control. We also test Belsky's differential susceptibility hypothesis by examining whether highly reactive infants are affected more than other infants by environmental predictors of EC. Last, we ask whether delay of gratification and motor control are differentially associated with three contemporaneous measures of socioemotional adjustment: externalizing, internalizing, and attention deficit behavior problems. Results should inform future interventions to improve children's EC. PUBLIC HEALTH RELEVANCE: This study addresses gaps in our knowledge about the antecedents and consequences of effortful control. Young children depend on effortful control, along with other facets of self-regulation, to manage behavioral impulses. Effortful control contributes to socioemotional, academic, and moral development, and is thus implicated in numerous public health problems such as attention deficit disorder, antisocial behavior, and health risk behaviors.